During the past few years, in the retail sales industry, it has become the general practice to make use of what is known in the packaging industry as "point of sales" packaging for the majority of products offered for sale in a retail outlet. This practice, as generally believed would be expected, has forced the packaging industry to not only develop but also to implement new equipment and operating practices. Such new equipment and operating practices being necessary to provide significant improvement in the quality of printing. The former "brown box", in other words, would no longer be an acceptable package for products offered for sale at the retail level.
As a result, flexographic printing was introduced into the package printing industry. Such flexographic printing is in widespread use at the present time. For example, see an article that was published in the December, 1979, issue of "Box Board Containers". The title of this article is "It's Time for a Change in Flexo". Generally, as mentioned in this article, flexographic printing entered this area of use in the 1960's. It was at this time that converters began installing the necessary equipment to implement use of the flexographic printing process. With their new flexographic printing equipment, the converters could now print, slot, fold, glue, die-cut and bundle in a true production line manner.
This change in equipment to the flexographic printing process also offered the converters a potential for extended capabilities and other improvements in package printing. Such extended capabilities being in addition to all the advantages of such in line operations. However, these additional benefits were not taken advantage of immediately. Even with this new process and equipment, for example, the converters continue to use the same printing plate systems that had been used prior to the introduction of such flexographic printing system. This printing plate system generally consisted of a relatively thick rubber plate material secured to a fabric which in turn was secured to a carrier material.
In the late 1970's and the early 1980's, a significant change in the printing plate systems in use in the package printing industry finally occurred. It was at that time that the Roger's Corporation introduced the use of a cellular polyurethane material as a backing for flexographic printing plates. In this particular system, there is a flexible printing plate secured directly to the upper surface of such polyurethane material which, in turn, is glued to the working surface of the printing plate cylinder. The gluing of such polyurethane material to the printing plate cylinder may be accomplished with either an adhesive film or what is known in the industry as "sticky back tape". In some cases, such polyurethane material may be adhered to and supported on a polyester backing material. In either case, however, the printing plate is secured directly to the upper surface of such polyurethane material. This can create some problems due to the difference in the coefficients of expansion.
In view of the fact that the printing plate system is essentially glued to the working surface of the printing plate cylinder, it is obvious that great care must be exercised during mounting of such printing plate system to the working surface of the printing plate cylinder to insure accurate alignment.
In the prior art, it is also known, to use a substantially T-shaped member to accurately align and secure one end of a printing plate composite to a bar-like member. This bar-like member is disposed on such working surface of the printing plate cylinder in a position substantially parallel to the longitudinal axis thereof. The printing plate, in this case, is disposed on a vinyl-like sheet. A back surface of such vinyl-like sheet is engaged with at least a portion of the working surface of such printing plate cylinder. Such T-shaped member is secured to one end of the vinyl-like sheet and the axially opposed other end of such vinyl-like sheet is usually secured to the printing plate cylinder with tape or strap-like members. This particular fastening system for the printing plate is commonly known in the package printing industry as the Matthews Fast-Loc System. Use of the Matthews Fast-Loc System generally results in reduced down time of the press being required so that proper alignment of the printing plate on the working surface of the printing plate cylinder can be achieved.
Even though each of the above discussed improved printing plate systems have greatly advanced the state of the art in the printing of such substrate materials used in the packaging industry, each of these systems also have certain limitations connected with their use. For example, the Roger's printing plate system requires a considerable amount of time being expended in set up in the press. This is the case even though the Roger's system has the benefit that it enables a poor quality substrate material to be used and is not as sensitive to slight imperfections, which may be present, in the working surface of the printing plate cylinder. The Matthews Fast-Loc printing plate system, on the other hand, can be set up rather quickly on the press. However, the Matthews Fast-Loc system normally requires a higher quality substrate material be used and is less tolerant of slight imperfections being present in the working surface of such printing plate cylinder.
It is also well known in the prior art to use a plurality of equally spaced grommets secured to one end of a printing plate carrier sheet. Such grommets enable rapid aligning and securing of one end of such carrier sheet of a working surface of a printing plate cylinder. These grommets fit over protruding pins secured to the printing plate cylinder adjacent the working surface thereof, as with the Matthews Fast-Loc System, use of this system known in the industry as the Dorr "Rapi-Die" will result in a significant reduction of the down time required in the printing arrangement to achieve the necessary alignment of the printing plate on the working surface of such printing plate cylinder, however, this system has the same drawbacks in that higher quality substrate material must be used and fewer imperfections in the working surface of such printing plate cylinder can be tolerated.